At first, its NOT POSSIBLE TO DOWNGRADE your PS Vita with this method. This method is just for updating a PS Vita with an old firmware, e.g. 1.06, to another old firmware, e.g. 1.81.
Or in other words: How to update your PS Vita to another firmware, which isnt the most recent one.

Things that are necessary for this method:

A PS Vita device with a lower per-installed firmware than the target FirmwarePS Vita Firmware filesNot necessary anymore! The PS Vita will just fetch them from my Zload.net server while updating!

The last step is the installation of the firmware. Grab your PS Vita, check if Wifi is disable and airplane mode enabled.

Everything looking fine? Great! Now reboot the PS Vita.

Open the CMA program at your PC and put the Vita usb cable into the Vita and the PC. Open the settings app at your PS Vita and click at the "system update" option.

Choose the "update via PC" option and your Vita should be able to find the target firmware. If the Vita says something like server outtime, or server error, you should check if Zload.net is online!

If everything is working like intended, then your PS Vita should find the "new" target firmware. Now install the firmware like usual. The firmware should install like every other firmware, and your PS Vita should reboot into the new target firmware, congratulations.

But what if the Vita does not update, says there is an error within the firmware or something similar?
If there are some problems, continue with the last emergency step, which should be working if you've done everything before correct.

Emergency Installation (Just in case the other method wasnt working!)

If the installation via Settings->Update->Update via PC is not working or does not install the new firmware properly, continue with this last step, the emergency installation!

This time we will use the Recovery Menu of the PS Vita for installing the firmware (For your information, you navigate with the keys of the Vita inside of the recovery menu, not with the touchscreen!).

For this type of installation are all 3 firmware images (rel, pre and sd) necessary, thats why the installation takes a bit longer than usually.

Shutdown the PS Vita (Hold the power button and select shutdown). Then start the PS Vita while holding this button combination:
PS-Button + R + Power button

Keep this combination pressed until the Vita starts. If you've done it correct, you should be in the Vitas recovery menu, if not, try it again.
You should see something like this:

Choose the 5th option, update system software. Next choose update via PC (CMA at your PC should be opened and your Vita should be connected via USB).

Now it will "prepare" for a very long time, depending on your internet connection and your download speed.

It will download all the 3 image files and will prepare them for your PS Vita device for a full update. This full update will install every 3 images at the PS Vita, for having a fully fresh new firmware at your Device, your settings and files wont be touched, dont worry.

After this full update, the Vita should have the target firmware installed and you should be able to use the new firmware.

Dutt wrote:I think The Z's method is way to hard for noobs..
I did not want to make a new topic for this as there's already one..

My Method..
1. Download and install "PS3.ProxyServer.GUI"
2. Start PS3.ProxyServer.GUI and Type in your PC's IP then select "PSP Mode" and click Start..
3. Click the Logs Tab, Then on your Vita Go to WiFi Settings and enter your PC's IP for the Proxy.
4. Go to System Update and click "Update Using Wi-Fi".. It will show the Latest Version then click "Next" and "Yes" Then "Do Not Accept" and "Yes".. This will give you the Link to the PUP file it will download and install..
5. Copy this link from the Logs screen and click "Replace File" Tab.. Past that link on the left side. On the Right side click the Little button and select the PUP file you want to install.
6. Now click the "Logs" Tab again and click "Update Using Wi-Fi" and make sure in the "Logs" Tab is says that the files has been Redirected to a local file.
7. Done you can update to any Version you want.. (You can not downgrade this way)

EDIT: I'm working on a Quick Video to help..

My old tutorial, which depended on owning an own server

At first, its NOT POSSIBLE TO DOWNGRADE your PS Vita with this method. This method is just for updating a PS Vita with an old firmware, e.g. 1.06, to another old firmware, e.g. 1.81.
Or in other words: How to update your PS Vita to another firmware, which isnt the most recent one.

If you wish to install firmware 2.12 or 3.01, feel free to grab these pre-packaged XML files, which will download said firmware from my server, so you can easily install those firmwares.
I do not offer this kind of service for any other kind of firmware, just for the 2.12 and 3.01!

If you use the pre-packaged XMLs for FW 2.12 or 3.01, you just have to install the right version of Sony CMA, the right version of OpenCMA and place the xml file in the right directory. - Then restart the CMA at your PC and restart the PS Vita. Open the Settings App and update via PC, it should now tell you that it found firmware 2.12/3.01 and wants to install it at yours. In case of doubt/errors, update via recovery menu (via PC).

At first we need our PS Vita device. We should be able to boot into the main menu and its recommended to disable every Wifi option at the device. Use the airplane mode AND disable Wifi, recommended.

Next we need the official Sony CMA (old version, pre-2.00 | or new version, post-2.00) which has to be patched with OpenCMA for using our little firmware update trick.WARNING: If you have the most recent version of the Sony CMA, it is necessary to have the PS Vita Firmware 2.00 or higher, but that is not what we want, use the older CMA + OpenCMA patch for this tutorial if you want to install a firmware below 2.00!

Grab the files for the wished Firmware from http://www.zload.net/ofw and save them in a folder, but do not unzip them, not now. (Downloading all 3 images (rel, pre and sd) recommended, additional information below!)

Grab the xml file for the wished Firmware from http://www.zload.net/ofw and save it in the same folder in which the firmware files are saved.

Now unzip the firmware files, the PUP file of the pre-Firmware zip, e.g. "PSVita OFW 1.81 (pre).zip" <- (This is just and example what the zip file can look like), has to be inside of a folder called PRE (or something else).

The PUP file of the sd-Firmware zip, e.g. "PSVita OFW 1.81 (systemdata).zip" <- (This is just an example what the zip file can look like), has to be inside of a folder called SD (or something else).

The PUP file of the Firmware zip (neither pre nor sd), e.g. "PSVita OFW 1.81.zip" <- (This is just an example what the zip file can look like), has to be inside of a folder called REL (or something else).

If you are done with unzipping and moving into the folders, upload them to your own server. You need an own server, its not possible without one. And the files has to be uploaded as .PUP files, not .ZIP files.

Modifying the XML file for for a proper usage:

This is one of the most important steps, the modifying of the XML file. Use the XML file which is for your wished firmware, e.g. 1.81 XML file for firmware 1.81.
I will use the 1.81 XML file as an example, you can use this tutorial for every XML file.

Now open the XML file with NotePad++ (or another editor, depends what you want to use) and change <region id="ru"> to <region id="eu"> (Use the region of your Device, mine is EU so i use EU).
Possible shortcuts: EU=europe, US=north america, SA=south america, RU=russia, JP=japan, AU=australia, KR=korea, and much more possibilities...

Next search for <version system_version="01.810.000" label="1.81"> and change it to <version system_version="09.990.000" label="1.81">.

The last necessary edit are the links of the files. In this XML file we can see a link with PRE a link with SD and a link with REL, that was the reason why you should use these names for the folders of the update files.

When you are done with editing the XML file, copy it as "psp2-updatelist.xml" into the CMA folder (which has to be patch with OpenCMA!). Now lets continue with the last step, the installation!

Installing the Firmware at the PS Vita:

The last step is the installation of the firmware. Grab your PS Vita, check if Wifi is disable and airplane mode enabled, ready? Okay!

Open the CMA program at your PC and put the Vita usb cable into the Vita and the PC. Open the settings app at your PS Vita and click at the "system update" option.

Choose the "update via PC" option and your Vita should be able to find the wished firmware. If the Vita says something like server outtime, or server error, you should better check if the links inside of the XML file are correct!

If everything is working like it should, should it be possible for your PS Vita to find the "new" wished firmware. Now install the firmware like usual. The firmware should install like every other firmware, and your PS Vita should reboot into the new wished firmware, congratulations.

But what if the Vita does not update, says there is an error within the firmware or something similar?
If there are some problems, continue with the last emergency step, which should be working if you've done everything before correct.

Emergency Installation (Just in case the other method wasnt working!)

If the installation via Settings->Update->Update via PC is not working or does not install the new firmware properly, continue with this last step, the emergency installation!

This time we will use the Recovery Menu of the PS Vita for installing the firmware (For your information, you navigate with the keys of the Vita, not with the touchscreen, inside of the recovery menu!).

For this type of installation are all 3 firmware images (rel, pre and sd) necessary, thats why i said you should download and upload all 3 of the images, not just the release image.

Shut the PS Vita down (Hold the power button and select shut down). Next start the PS Vita with this button combination:
PS-Button + R + Power button

Keep this combination pressed until the Vita starts. If you've done it correct, you should be in the Vitas recovery menu, if not, try it again.
You should see something like this:

Choose the 5th option, update system software. Next choose update via PC (The CMA should be opened).
Now it will "prepare" a very long time, depends on your internet connection and your download speed.
It will download all the 3 image files and will prepare them for your PS Vita device for a full update. This full update will install every 3 images at the PS Vita, for having a fully fresh new firmware at your Device, your settings and files wont be touched, dont worry.